White (1887), referring to Arctium officinalis, noted that the rough leaves have been used as a rubefacient, and that parts of the burs mixed with the seeds irritated workmen unless they stood to windward. The rough hairs can produce irritation of the skin (Sidi 1951) and of the cornea (Grant 1974). The effects on the eye are both mechanical and toxic (Bruhn 1938, Havener et al. 1955, Breed & Kuwabara 1966). The barbed needles attached to the seeds are responsible rather than the outer shafts that hook onto clothing (Duke-Elder & MacFaul 1972b). A statement that the leaves can produce contact dermatitis (Massey 1941) requires confirmation.

Frain-Bell & Johnson (1979) observed positive patch test reactions to the oleoresin of the species in 2 from 55 patients with the photosensitivity dermatitis and actinic reticuloid syndrome. Phototoxic activity of an extract of burdock against two of three test micro-organisms was demonstrated by Wat et al. (1980b).

The potentially allergenic sesquiterpene lactone arctiopicrin has been reported to occur in this species.

The species is a native of South Africa, adventive to Australia (Hand 1944). Dermatitis occurred from contact with the plant (Farmer 1941, Hand 1944); the essential oil of the plant produced a positive patch test reaction in one case when diluted 1 in 100 but, in a second case, a generalised flare-up of dermatitis occurred (Hand 1944). The fresh plant is irritant by closed patch test in almost every case tested (Burry 1973). Burry et al. (1973) observed positive patch test reactions to an extract from the plant in 1 of 13 patients with "Australian bush dermatitis". Cross-sensitivity to various Chrysanthemum L., Xanthium L., Olearia Moench, and Inula L. species was also observed. Burry (1979) observed a positive patch test reaction to this species in a patient with "fleabane dermatitis" (see Conyza bonariensis Cronq.).

Burry & Kloot (1982) believe that Australian bush dermatitis is caused by airborne dusts from members of the Compositae, formed from the breakdown of senescent tissues in the hot, dry conditions of the bush, and that capeweed (A. calendula) is one of the specific elicitors of this condition. These authors also give a distribution map for this species in Australia.

Burry (1980a) observed a weakly positive patch test reaction to this species in a 75 year old patient who had been admitted to hospital with a severe exacerbation of a condition that had been diagnosed 4 years previously as photodermatitis.

Arnica chamissonis Less. sspgenuina Maguire

Two potentially allergenic pseudoguaianolides have been reported from this taxon (Willuhn et al. 1981). The subspecies genuina, foliosa, and incana can be distinguished from one another by the sesquiterpene lactones present in each (Willuhn & Herrmann 1978).

Arnica foliosa Nutt.

The potentially allergenic sesquiterpene lactones arnifoline and carabrone have been reported from this species. See Arnica longifolia.

Arnica longifolia Eaton

Three persons isolating sesquiterpene lactones from the flower heads of this species developed an occupational allergic contact dermatitis. The sensitising compounds were found to be the sesquiterpene lactones carabrone, helenalin,and acetylhelenalin. Cross-reactivity to Arnica montana L., Chrysanthemum indicum L., apoludin, ambrosiol, burrodin, and coronopilin was also observed (Hausen et al. 1978c).

Arnica montana L.

Mountain Tobacco, Wolf's Bane

The plant has long been used in the form of a tincture (of either the dried flowerheads or the rhizomes) for local application to bruises and sprains (Muillot 1899, Biberstein 1927, Hausen & Schulz 1973, Stuart 1979), but is of doubtful value and may produce severe dermatitis (Wade 1977). Ingestion of the flowerheads has produced severe gastrointestinal symptoms (Wade 1977). Most of the reports of dermatitis from Arnica originate from Europe. Arnica allergy was reviewed by Hausen (1980a).

Tincture of Arnica, which is an alcoholic extract, has been known to be capable of producing dermatitis since the 19th Century. According to White (1887), Hebra had seen many such cases and recommended to those who advocated its use that homeopathic amounts be made up, that is "a drop of the tincture to a pail of water". White (1887) also quoted Fox as stating in 1873 that "arnica may produce erythema and swelling of the part to which it is applied, or it may excite a real eczema"; the root as well as the flowerhead was "irritant". Phillips (cited by Morrow 1893) asserts that the irritant effects of arnica never follow the use of an aqueous solution which contains none of the volatile oil from the plant. Arnica tincture in contact with the eye has caused oedema of the lids and hyperaemia of the conjunctiva, but has not been considered to be injurious to either the cornea or the conjunctiva (Grant 1974). Harrison (1906) included arnica in a list of drugs, applied externally or taken internally, which may cause dermatitis.

Piffard (1881), citing earlier observations made by Mercier in 1811, contemplated the possibility that the irritant actions of arnica preparations are attributable to infestation of the flowers used in their preparation with the larvae of Atherix maculatus. This was further rationalised by his own observation that tinctures prepared from arnica root seemed not to possess the acrid and irritating properties of the tincture prepared from the flowers.

Cross-sensitivity between Arnica and Chrysanthemum L. has been observed (Paschoud 1965, Hausen 1979).

A number of sesquiterpene lactones have been isolated from Arnica montana, including helenalin and its acetate and methacrylate, arnifoline, carabrone, and xanthalongin. Helenalin and its esters have proved to be the primary sensitisers (Hausen 1980a).